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Abstract:

A limb for a breathing circuit manufactured from very thin walled polymer
materials has an elongate axial reinforcing spine lying freely inside the
conduit and fixed to each end connector. The spine is laterally compliant
but axially stiff. The spine provides resistance to tensile and
compressive loads on the conduit, including that induced by prevailing
internal pressures.

Claims:

1. A limb for a breathing circuit comprising:a very thin walled flexible
conduit having a first end and a second end and a breathing gases pathway
therebetween,a first connector fixed to said first end of said conduit,a
second connector fixed to said second end of said conduit, andan elongate
reinforcing member lying freely within said very thin walled conduit
along a non-tortuous path from one end of said conduit to the other end
of said conduit, and connected with said first connector and said second
connector, such that said reinforcing member substantially improves the
axial stiffness of said conduit, and whereinsaid elongate reinforcing
member does not include a passageway large enough for gases delivery to a
patient.

2. A limb for a breathing circuit as claimed in claim 1, wherein said
elongate reinforcing member has a cross sectional area, measured from the
outer perimeter, less than 10% of the cross sectional area of the bore of
said breathing conduit.

3. A limb for a breathing circuit as claimed in claim 1, wherein said
elongate reinforcing member is hollow, and said hollow elongate
reinforcing member is blind terminated at each end by said first
connector and said second connector.

4. A limb for a breathing circuit as claimed in claim 2, wherein said
hollow elongate reinforcing member is hollow and said hollow member is
large enough to be used as a pressure measurement or feedback conduit.

5. A limb for a breathing circuit as claimed in claim 2, wherein said
elongate reinforcing member has a solid, substantially circular cross
section, and two ends.

6. A limb for a breathing circuit as claimed in claim 2, wherein said
elongate reinforcing member includes a positive temperature coefficient
heating element.

7. A limb for a breathing circuit as claimed in claim 2, wherein said
elongate reinforcing member includes a resistance heating element.

8. A limb for a breathing circuit as claimed in claim 2, wherein the
length of said elongate reinforcing member is between 100.5% and 105% of
the length of said conduit.

9. A limb for a breathing circuit as claimed in claim 1, wherein said
connectors have a first end suitable for making connection with auxiliary
equipment and a second end for making connection with a breathing
conduit, andan annular shoulder between said first end and said second
end,said second end extending along an axis and having a substantially
circular cross section, andsaid second end having at least one protrusion
on an outer surface for interlocking engagement with a helical rib of a
breathing conduit.

10. A limb for a breathing circuit as claimed in claim 9, wherein said
protrusion is an external thread having a pitch suitable for engagement
with said helical rib of a breathing conduit.

11. A limb for a breathing circuit as claimed in claim 9, wherein said
shoulder portion has an annular recess for receiving a securing collar
having an extrusion axis.

12. A limb for a breathing circuit as claimed in claim 9, wherein said
second end of said end connector has a recess substantially parallel with
said axis for receiving said elongate reinforcing member.

13. A limb for a breathing circuit as claimed in claim 11, wherein said
securing collar has a recess substantially parallel with said extrusion
axis for receiving said elongate reinforcing member.

14. A limb for a breathing circuit as claimed in claim 1, wherein said
elongate reinforcing member is resilient and does not plastically deform
in use, under normal flexing and bending of said limb.

15. A limb for a breathing circuit as claimed in claim 1, wherein said
elongate reinforcing member has a cross sectional area between 3 mm2
and 12.5 mm.sup.2.

16. A limb for a breathing circuit as claimed in claim 1, wherein said
elongate reinforcing member has a minimum bending stiffness between 693
Nmm2 and 11096 Nmm.sup.2.

17. A limb for a breathing circuit as claimed in claim 1, further
comprising:a braided sheath surrounding said conduit and being fixed at
and around one end to said first connector and at and around its other
end to said second connector.

18. A limb for a breathing circuit as claimed in claim 17, wherein said
sheath is a braided tube braided from polyethylene terephthalate
monofilaments.

19. A method for manufacturing a limb for a breathing circuit
comprising:providing a very thin walled flexible breathing conduit having
a first end and a second end,locating an elongate reinforcing member
having a first and a second end, lying freely within said conduit along a
non-tortuous path from one end of said conduit to the other end of said
conduit,fixing a first end connector with a first end of said breathing
conduit, and a first end of said elongate reinforcing member, andfixing a
second end connector with said second end of said conduit and said second
end of said elongate reinforcing member, such that said reinforcing
member substantially improves the axial stiffness of said conduit, and
whereinsaid elongate reinforcing member does not include a passageway
large enough for gases delivery to patient.

20. A method for manufacturing a limb for a breathing circuit as claimed
in claim 19, further comprising:locating a reinforcing mesh having a
first and a second end, over the outside of said breathing conduit,fixing
a first end connector with a first end of said breathing conduit, and a
first end of said reinforcing mesh, andfixing a second end connector with
said second end of said conduit and said second end of said reinforcing
mesh.

Description:

CROSS-REFERENCE

[0001]This patent application is a continuation of U.S. patent application
Ser. No. 10/653,821, filed Sep. 3, 2003, and entitled "LIMB FOR BREATHING
CIRCUIT". This application is hereby incorporated by reference.

BACKGROUND TO THE INVENTION

[0002]The present invention relates to components for breathing circuits
and in particular to limbs for breathing circuits.

SUMMARY OF THE PRIOR ART

[0003]In assisted breathing, particularly in medical applications, gases
are supplied and returned through conduits. Such conduits are ideally
light and flexible to ensure the greatest level of comfort for the
patient.

[0004]As taught in our prior patent application AU 43823/01 thin membrane
walls are particularly used in breathable membrane applications where the
passage of water vapour through the membrane but not the passage of
liquid water is desired.

[0005]Thin walled conduits may include helical or annular reinforcing ribs
which improve resistance to crushing and pinching, while still allowing
the conduit to be flexible in order to maintain patient comfort. A
disadvantage of these types of flexible conduits is their lack of
stiffness. The extremely thin walls of these types of conduits provide
very little resistance to tensile, compressive or torsional forces. While
annular or helical ribs, whether inside, outside or between layers of the
conduit wall, do provide some longitudinal stiffness, these conduits are
still prone to large axial displacements both compressive and tensile.
This can lead to substantial internal volume changes under fluctuating
breathing pressures, potentially significant enough to disrupt automated
ventilation. Our prior art patent application taught provision of
external longitudinal reinforcing in the form of a set of axial polymer
threads bonded to the radial support bead. However these have the
disadvantage of being easily caught or snagged.

[0006]A further disadvantage of very thin walled conduits is a reduced
durability of the very thin membrane making up the walls of the conduit.
The very thin membrane may be more susceptible to piercing from sharp
objects and/or plastic deformation from tensile forces.

SUMMARY OF THE INVENTION

[0007]It is an object of the present invention to provide a limb for a
breathing circuit, which will at least go some way towards improving on
the above or which will at least provide the public and the medical
profession with a useful choice.

[0008]Throughout this specification the term very thin walled conduit
means a conduit where under the intended prevailing conditions the
conduit would be subject to excessive axial compression, e.g. a conduit
formed according to a method as described in U.S. Pat. No. 3,910,808
using a SYMPATEX film having a thickness less than 50 microns.

[0009]In one aspect the invention consists in a limb for a breathing
circuit comprising:

[0010]a very thin walled conduit having a first end and a second end and a
breathing gases pathway therebetween,

[0011]a first connector fixed to said first end of said conduit,

[0012]a second connector fixed to said second end of said conduit and

[0013]an elongate reinforcing member lying freely within said very thin
walled conduit along a non-tortuous path from one end of said conduit to
the other end of said conduit, and connected with said first connector
and said second connector.

[0014]Preferably said connectors have a first end suitable for making
connection with auxiliary equipment and a second end for making
connection with a breathing conduit, and

[0015]an annular shoulder between said first end and said second end,

[0016]said second end extending along an axis and having a substantially
circular cross section, and

[0017]said second end having at least one protrusion on an outer surface
for interlocking engagement with a helical rib of a breathing conduit.

[0018]In a further aspect the invention consists in a method for
manufacturing a limb for a breathing circuit comprising:

[0019]providing a very thin walled breathing conduit having a first end
and a second end,

[0020]locating an elongate reinforcing member having a first and a second
end, lying freely within said conduit along a non-tortuous path from one
end of said conduit to the other end of said conduit,

[0021]fixing a first end connector with a first end of said breathing
conduit, and a first end of said elongate reinforcing member, and

[0022]fixing a second end connector with said second end of said conduit
and said second end of said elongate reinforcing member.

[0023]In a further aspect the invention may broadly be said to consist in
a limb for a breathing circuit comprising:

[0024]a very thin walled conduit having a first end and a second end,

[0025]a first connector fixed to said first end of said conduit,

[0026]a second connector fixed to a second end of said conduit, and

[0027]a braided sheath surrounding said conduit and being fixed at and
around one end to said first connector and at and around its other end to
said second connector.

[0028]In a further aspect the invention consists in a method for
manufacturing a limb for a breathing circuit comprising:

[0029]providing a very thin walled breathing conduit having a first end
and a second end,

[0030]locating a reinforcing mesh having a first and a second end, over
the outside of said breathing conduit,

[0031]fixing a first end connector with a first end of said breathing
conduit, and a first end of said reinforcing mesh, and

[0032]fixing a second end connector with said second end of said conduit
and said second end of said reinforcing mesh.

[0033]To those skilled in the art to which the invention relates, many
changes in construction and widely differing embodiments and applications
of the invention will suggest themselves without departing from the scope
of the invention as defined in the appended claims. The disclosures and
the descriptions herein are purely illustrative and are not intended to
be in any sense limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

[0034]FIG. 1 is a cross sectional side elevation of a single walled
breathing conduit formed by applying a molten reinforcing bead on top of
overlapping spirally wound thin film layers.

[0035]FIG. 2 is a cross sectional side elevation of a double walled
breathing conduit formed in a manner analogous to the conduit shown in
FIG. 1.

[0036]FIG. 3 is a plan view of a conduit forming device for forming the
conduit depicted in FIG. 2.

[0037]FIG. 4 is a cross sectional side elevation of a single walled
breathing conduit formed by applying a molten reinforcing bead so that it
resides between the overlapping spirally wound thin film layers.

[0038]FIG. 5 is a plan view of a conduit forming device for forming the
conduit depicted in FIG. 4.

[0039]FIG. 6 is an assembly perspective view of one end of a breathing
limb according to a preferred embodiment of the present invention.

[0040]FIG. 7 is a partially assembled perspective view of the end of a
breathing limb shown in FIG. 6.

[0041]FIG. 8 is a cross-sectional elevation of the ends of the breathing
limb according to FIGS. 6 and 7.

[0042]FIG. 9 is an assembly perspective view of one end of a breathing
limb according to a further preferred embodiment of the present
invention.

[0043]FIG. 10 is a cross-sectional elevation of a breathing limb according
to a further preferred embodiment of the present invention.

[0044]FIG. 11 is a partially assembled perspective view of one end of a
breathing limb according to a further aspect of the present invention
including an outer reinforcing mesh.

[0045]FIG. 12 is cutaway view of the breathing limb of FIG. 11 showing the
outer reinforcing mesh fixed at and around the end connectors.

DETAILED DESCRIPTION

[0046]The present invention relates to breathing conduits in general and
in particular to methods of providing reinforcement for very thin walled
conduits used to provide a closed pathway for delivering gases to a
patient. Consequently the present invention finds application in
breathing conduits fabricated from a variety of different materials and
manufactured by a variety of different methods. The conduits may be
single or multiple walled and may include breathable walls or portions of
breathable wall.

[0047]As a corollary of material cost and/or breathability of the material
it is preferred that the conduit wall be manufactured to have a very thin
wall, so much so that the conduit wall membrane may be insufficiently
sturdy to be self supporting. Spiral or helical or annular reinforcing
members may be provided on the tubular membrane to provide support
against crushing and pinching. The helical, spiral or annular supporting
members may for example be formed from polymer plastic materials, such as
the material used in the wall of the conduit or having the same base
polymer. It has been found that breathing conduits such as those
described above are extremely light, flexible and provide good crush
resistance, however the conduits may also have reduced resistance to
axial deformation. Due to the very thin polymer film forming the walls of
the conduit, the resulting breathing circuit limb may have reduced axial
stiffness and may be prone to expansion, and contraction along the axis
of the conduit, due to axial or torsional forces. In use, axial forces
arising from patient breathing may produce expansion and/or contraction
along the length of the limb. In one aspect the present invention
provides a breathing circuit limb with improved axial stiffness. In a
further aspect the present invention provides a breathing circuit limb
with improved torsional stiffness.

[0048]Very thin walled breathing conduits such as those described above
can be fabricated by a number of different methods. The following
describes several very thin walled conduits and associated methods of
manufacturing very thin walled conduits to which the present invention
may be applied.

[0049]Referring to FIG. 1 a cross section of the wall of a breathing
circuit limb is shown in which the flexible wall of the conduit is formed
from a very thin film plastic membrane, and wound helically with edges of
adjacent turns welded together by a reinforcing bead. Supplied as tape,
either pre-formed or extruded online, the very thin film 40 is wound
helically onto a former with adjacent edges 41 and 42 of tape
overlapping. A helical supporting rib 43, provided in a molten state is
then laid on top of the overlap between adjacent turns. The helical
supporting rib thermally and mechanically bonds the two adjacent strips
with the rib forming a flexible resilient conduit once cooled. The
resulting product is a single walled breathing conduit which is light and
flexible. Further embodiments of conduits formed by such a process, such
as multiple walled conduits, can be formed by adding further stages to
the above described forming process.

[0050]Referring to FIG. 2 a double walled conduit may be formed by adding
an additional thin film layer 44 and supporting rib 45.

[0051]An example of forming apparatus suitable for manufacturing the
double walled breathing tube product according to the embodiment
described in FIG. 2 is shown in FIG. 3. The apparatus includes a former 1
preferably of a known type including a plurality of rotating rods
arranged around a central support rod. The rods extend from and are
rotated by a gearbox within a machine stock 2. At least in the tube
forming region the rotating rods follow a helical path. The pitch angle
of the rods relative to the support rod controls the pitch angle of the
tube being formed. An example of such a machine is a spiral pipeline
mandrel available from OLMAS SRL of Italy. Tube being formed on the
former is rotated and advanced in the direction of arrow 3 by the
movement of the rotating rods. The advance speed of the former is
selected relative to the rotational speed so that the pitch of the
helical laying of the strip or tape on to the former 1 is a little less
than the width of the strip so that adjacent turns narrowly overlap. A
first extruder 4 extrudes a very thin tape 5 of breathable polymer
materials. The tape 5 deposits on the former 1 in a helical fashion by
action of the former. The pitch of the helical deposition of tape 5 is
slightly less than the width of tape 5. The helical deposition of tape 5
forms the inner breathable wall 6 of the conduit. A second extruder 7
extrudes a bead 8 of polymer material. The bead 8 deposits on the former
over the joint or overlap between adjacent turns of tape 5 forming a
raised bead 9 along this join and welding the overlapping turns of tape
5, A third extruder 10 extrudes a second tape 11 of breathable polymer.
The second tape 11 of breathable polymer is deposited on the former 1 to
span between adjacent turns of bead 8. Adjacent turns of tape 11 overlap,
forming outer breathable sheath 12. A fourth extruder 13 extrudes a
second molten polymer bead 14. The bead 14 is helically deposited along
the overlap between adjacent turns of the second tape 11 and welds the
overlapping turns of tape 11. In addition to the bonding of the film
overlap by application of the molten bead other active fusing techniques
may be applied.

[0052]The resulting product is a double walled reinforced breathing
conduit with a space between the inner and outer walls. The breathing
conduit of FIG. 2 is manufactured by a method analogous to the method
employed to manufacture the conduit of FIG. 1. The forming apparatus
shown in FIG. 3 is effectively made up of two identical stages arranged
in series.

[0053]The first stage of the former shown in FIG. 3 consists of film
extruder 4 and bead extruder 7. Film 4 is wound around former 1 while
extruder 7 extrudes a molten bead on top of the overlapping layers of
film 5, resulting in a conduit such as that shown in FIG. 1. The second
stage consists of film extruder 10 and bead extruder 13. This second
stage effectively repeats the first stage over top of the conduit formed
by the first stage and results in the double walled breathing conduit of
FIG. 2.

[0054]Referring to FIG. 4, a conduit is shown according to another
preferred method of manufacture of single walled breathing conduits. This
method is particularly suited to very thin walled conduits and is the
subject of a co pending patent application. The very thin film is
arranged in a spiral or helix such that the edge portions of adjacent
layers overlap and form the wall of a tube. Interposed the overlapping
edges of adjacent winds of film is a bead of polymer material 47 bonded
with the overlapping portions of film sealing the joint between windings
and forming a continuous tube. The seam is formed between the edge of a
first layer of film 48 and the edge of a second, adjacent layer of film
46 which is laid over top of the polymer bead while the bead is molten.
The overlapping layer of film because it is so thin, follows the contour
of the bead very closely and results in a smooth inner conduit wall.

[0055]An example of forming apparatus suitable for manufacturing the
breathing tube according to an embodiment of the present invention
described in FIG. 4 is shown in FIG. 5. The apparatus includes a former
15 including a plurality of rotating rods arranged around a central
support rod. The rods extend from and are rotated by a gearbox within a
machine stock 16. At least in the tube forming region the rotating rods
follow a helical path. The pitch angle of the rods relative to the
support rod controls the pitch angle of the tube being formed. An example
of such a machine is a spiral pipeline mandrel available from OLMAS SRL
of Italy.

[0056]Tube being formed on the former is rotated and advanced in the
direction of arrow 17 by the movement of the rotating rods. The advance
speed of the former is selected relative to the rotational speed so that
the pitch of the helical laying of the strip or tape on to the former 15
is a little less than the width of the strip so that adjacent turns
narrowly overlap. A first extruder 18 extrudes a tape 19 of very thin
film polymer materials. The tape 19 deposits on the former 15 in a
helical fashion by action of the former. The pitch of the helical
disposition of tape 19 is slightly less than the width of tape 19. The
helical deposition of tape 19 forms the wall 20 of the conduit. A second
extruder 21 extrudes a bead 22 of polymer material. The molten bead 22
deposits between the overlapping portions of adjacent winds of tape 19
and is sufficiently heated to weld to the strips of tape 19. Applying the
molten bead between the overlapping layers of tape may improve the weld
quality as both layers of tape that are to be welded are in physical
contact with the molten bead. The quality of the surface finish for the
inner surface of a breathing conduit is important, as a rough inner
surface may hinder gases flow and contribute to more condensation to
building up in the conduit. The above described construction technique is
especially suited to conduits fabricated from very thin film. The thin
film is able to conform to the shape of the raised rib of the applied
molten bead 22 during fabrication. By lapping very closely onto the bead
and wrapping around the bead) the very thin film maintains a smooth inner
surface on the finished conduit product as shown in FIG. 4.

[0057]In addition to the bonding of the film to the molten bead between
adjacent over lapping layers, other active fusing techniques may be
applied. Active methods may include hot air welding, hot rollers or radio
frequency welding.

[0058]It will be appreciated that the above described breathing conduits
and methods of manufacture are provided as examples of the type of very
thin walled conduits to which the present invention may be applied. The
examples have been chosen to illustrate the many possible variations and
are not meant to be in any way limiting. Many further variations will
present themselves to those skilled in the art. While some embodiments of
the present invention have been described as preferred and convey
particular advantages over other embodiments many other combinations may
prove commercially useful.

Such variations may include: [0059](a) the utilisation of breathable
material for the conduit walls or parts of the walls; [0060](b) single
walled or multiple walled conduits, with or without space between the
walls may be formed by adding extra stages to the forming process;
[0061](c) single layer or multiple layer walls; [0062](d) very thin tape
may be extruded at the time of forming, or pre-formed and supplied to
former on reels; [0063](e) very thin tape may be provided as a laminate
having a very thin film layer and a reinforcing layer which is also
permeable to water vapour; [0064](f) forming process may include a
secondary thermal welding process; [0065](g) molten bead may interpose
layers or be applied on top of two or more layers; [0066](h) direct
extrusion or drawing or blowing of a conduit; [0067](i) forming a conduit
from a very thin film with a longitudinal seam; [0068](j) providing a
series of annular radial support beads rather than a helical radial
support bead.

[0069]The present invention may be broadly described as relating to
methods of reinforcing breathing circuit limbs so as to provide increased
axial or torsional stiffness, or both. While the present invention is
particularly suited to conduits having very thin walls, it will be
readily appreciated that application may also be found in more
traditional conduits if further reinforcement is desirable. The first
preferred embodiment of the present invention describes the provision of
an axial spine and end connector whose primary function is to improve the
axial stiffness of a breathing circuit limb. The second preferred
embodiment of the present invention describes an external reinforcing
sheath or mesh and an end connector for use with such reinforcing in a
breathing circuit limb. The reinforcing mesh is bonded to the limb at
only the ends of the limb where the conduit wall inserts into the end
connector. It will be appreciated from the following description that the
end connectors described are suitable for use with either one, or both,
of the preferred embodiments of the present invention. While each
embodiment of the present invention is discussed in turn, it is in no
sense meant to be limiting as the preferred embodiments may be employed
separately or together.

[0070]A first preferred embodiment of a breathing limb according the
present invention will be described in detail with reference to FIGS. 6
to 8. The breathing limb has a conduit end connector 23 (or 49), suitable
for connecting a breathing conduit with a device, for example a gases
humidification device or ventilator or mask. A first end of end connector
23 is configured to mate with auxiliary equipment such as a ventilator or
mask, while the second end is configured to extend into a breathing
conduit. The end view cross section of each end portion of the connector
is substantially circular. Between the two ends of the end connector 23
is a shoulder region which makes the transition between the respective
diameters of the connector ends. Preferably the shoulder portion has an
annular recess 32, for receiving a securing collar or retaining sleeve
29.

[0071]The limb includes an elongate reinforcing member or spine 24 lying
freely within conduit 25. Conduit 25 for example, is such as those
described above. The second end of conduit end connector 23 has a recess
26 adapted to receive an elongate reinforcing spine or rod 24. The spine
24, runs the length of the conduit from the connector 23 at one end of
the tube, down the inside of the conduit, and is secured in another end
connector 49 at the other end of the conduit. Preferably the spine is
substantially the same length as the conduit and follows a non-tortuous
path between the connectors. Because the spine (between the connectors)
is preferably slightly longer than the conduit, it will not follow a
linear path, but rather will bend into a shallow wavy and/or spiral form.
It will also be appreciated that a spine slightly shorter than the
conduit will also result in a degree of axial reinforcement. When
assembled as described the combination of end connector and spine will
provide the breathing conduit with additional axial stiffness, by
potentially taking some of the axial forces and will therefore go some
way to overcoming the above described disadvantages that arise from the
use of breathing conduits having extremely thin film walls. In this
embodiment it is preferable to choose the reinforcing spine (material,
gauge and number) to be sufficiently stiff to resist buckling under the
transiently reduced internal pressures that could be expected during
patient breathing and sufficiently stiff to provide improved axial
stiffness to the conduit. Preferably the elongate reinforcing member is
manufactured from high density polyethylene having a Young's modulus (E),
of approximately 0.88 GPa. Preferably the elongate reinforcing member has
a cross sectional are between 3 mm2 and 12.5 mm2. Preferably
the elongate reinforcing member has a minimum bending stiffness
(EI=Young's Modulus*Second Moment of Area) for its cross section between
693 Nmm2 and 11,096 Nmm2.

[0072]Although embodiments containing only one elongate reinforcing spine
are shown, it will be appreciated by those skilled in the art that the
end connectors described could easily be modified to accommodate multiple
reinforcing spines. In such multi-spine embodiments, care needs to be
taken to ensure that the gases flow is not disrupted too detrimentally. A
further important consideration when choosing the material, gauge and
number of reinforcing members is to ensure that the breathing circuit
limb remains laterally flexible and thus maintain patient comfort.

[0073]The reinforcing spine is preferably made from a suitable approved
plastic material, such as high density polyethylene, or the same material
as the end connectors if welding of the spine and end connectors is
selected for manufacture. In the preferred embodiment the reinforcing
spine has a circular cross section to minimise any potential stress
raisers. The spine may be made from a variety of materials, and may have
a variety of cross sections being either solid or hollow without
departing from the spirit of the present invention. Preferably in hollow
spine embodiments the spine is blind terminated at each end by the end
connectors. If the spine is hollow and has a narrow bore, the size of the
bore will be insufficient for general gases flow or gases delivery. The
cross sectional area of the spine (measured from the outer perimeter of
the cross section of the spine) is preferably less than 10% of the cross
sectional area of the bore of the conduit so that gases flow is not
significantly disrupted. While the spine diameter is not large enough to
facilitate significant gases flow (to a patient for example) it may be
used for other purposes such as pressure measurement, or pressure
feedback. The spine may also include a heater element such as a PTC
(Positive Temperature Coefficient) heater or a resistance heating
element.

[0074]It is envisaged that there are several possible variants which may
be employed to secure the reinforcing spine and/or reinforcing mesh into
each of the end connectors of the breathing circuit limb. The general
requirements for the end connectors are as follows. The end connectors
must provide a means for securely fastening the spine and/or reinforcing
mesh so as to prevent pull out during use. Preferably the end connectors
are constructed such that assembly of the components during manufacture
can be achieved easily. A further consideration is that the end connector
when fastened to a breathing conduit to form the finished product should
be neat tidy and preferably appealing to the eye of an end user. The
following describes two alternative preferred embodiments of the present
invention which attempt to satisfy the abovementioned design objectives.
It will be appreciated that the portion of the end connector described
which connects to equipment such as a ventilator or mask may be male,
female or an androgynous type connector without departing from the
present invention. Further, each end of a conduit may have the same or a
different type of connector according to what type of connection is
required. If a heater wire is included in the breathing circuit limb
(whether associated with the reinforcing spine or not) the end connector
at least one end will preferably be adapted to make an electrical
connection together with the gases pathway connection.

[0075]Referring to FIGS. 6 to 8, a connector according to a preferred
embodiment of the present invention is shown. In order to provide a
strong bond between the conduit and the connector, a portion of the
connector which receives the conduit is provided with outer raised
protrusions 28 to cooperate with the helical reinforcing bead of the
conduit. The protrusions 28 are arranged to cooperate with the pitch of
the conduits helical reinforcing bead and preferably take the form of a
continuous thread. It will however be appreciated that the protrusions
may be any number of discrete bumps arranged to cooperate with the
conduit reinforcing bead. The raised thread 28 takes up a position
between the adjacent turns of the helical reinforcing bead 35 of the
conduit. The thin wall of the conduit between the reinforcing bead is
able to deform if necessary to accommodate the raised external thread of
the end connector locking the components together. These features provide
a mechanical connection and resistance to the conduit being pulled from
the connector. As shown in FIG. 6 the portion of the connector which
receives the conduit is also provided with a recess or groove 26 for
receiving the reinforcing spine 24. Preferably the recess 26 is
substantially parallel with the extrusion axis of the connector. For
assembly, the recess 26 provides a locating means for the reinforcing
spine allowing the conduit to be threaded over the external raised thread
on the receiving portion of the end connector. The reinforcing spine runs
up the inside of the conduit and is received into recess 26 of the end
connector. The spine then emerges from the recess 26 where an end portion
36 of the spine 24 is folded back on itself around the outside of the
conduit wall. This feature provides a mechanical interlocking of the
spine around the conduit wall as well as providing an end section of the
spine that is in a position to be adhesively secured to the outer surface
of the conduit wall.

[0076]In one preferred embodiment, illustrated in FIG. 6, a retaining
sleeve or securing collar 29 is fitted over the assembled components. The
securing collar 29, is substantially cylindrical about an extrusion axis.
The retaining sleeve may include a raised portion 30 which results in a
recess on the inside of the securing collar as shown in FIGS. 6 to 8 for
receiving the end portion of the spine 24 which is folded back on itself
on the outside of the breathing conduit. Alternatively a recess may be
formed on the inner wall of the securing collar 29, without the presence
of an external protrusion. Preferably the recess is substantially
parallel with the extrusion axis of the securing collar. Alternatively,
referring to FIG. 9 the end portion of the spine 36 may be folded so it
lies between the helical reinforcing bead 35 of the conduit and the
raised thread 28 of the end connector 23.

[0077]The assembly is secured via a tubular retaining or securing collar
sleeve 31. The retaining sleeve 31 and end connector 23 may be provided
with a positive initial location via a snap fit interaction between a
snap fit portion 32 of the end connector 23 and the lip of retaining
sleeve 31. Referring to FIGS. 6 to 9, a suitable adhesive such as EVA
(Ethylene-Vinyl Acetate) glue can then be injected into the annular space
33 formed between the receiving portion of the end connector and the
retaining sleeve. One or more small openings may be provided in the
securing collar for the purpose of injecting glue into the annular cavity
33. The injected adhesive performs two functions, firstly the adhesive
forms a seal between the conduit and the end connector. Secondly, the
adhesive forms both an adhesive bond and a mechanical bond anchoring the
conduit and spine to the end connector. The mechanical bond is formed
between the raised external threads of the end connector and the cured
glue which fills the annular space between the end connector and the
retaining sleeve. The mechanical bond between the raised threaded portion
of the end connector and the breathing conduit is an important feature
because there may be no adhesive between these two surfaces. The cured
glue must be hard enough to prevent the thin walled conduit and
reinforcing bead from deforming far enough to allow the conduit to be
pulled over the raised external thread.

[0078]An alternative preferred embodiment of an end connector will be
described with reference to FIG. 10. An end connector as described
previously with an external raised thread 28 on a conduit receiving
portion of the connector is provided. In a similar manner to that
described above the end connector is also provided with a recess 26 for
receiving a reinforcing spine. During assembly the reinforcing spine is
located in the recess before the helically ribbed breathing conduit is
threaded over the reinforcing spine and receiving portion of the end
connector. As described above, an end portion of the reinforcing spine 36
is folded over the outside of the breathing conduit wall in preparation
for adhesive securing. Alternatively, end portion 36 may be positioned as
shown in FIG. 9. The assembly is then inserted into an injection mould
cavity so that a collar 38 (shown hatched) is overmoulded to perform the
functions of securing and sealing as described above.

[0079]Due to the axial compliance of very thin walled conduits, the length
of spine will contribute to the determination of the length of the limb.
In the preferred embodiment the spine length is chosen such that when
fitted inside the conduit and secured to the respective end connectors,
the conduit is elongated such that the conduit length is close to its
maximum length (preferably within the elastic limit of the conduit
walls). In such a condition the wrinkling of the conduit wall is reduced,
improving the performance of the breathing circuit limb without putting
undue stress on the conduit wall due to axial tension generated by the
spine. The axial stiffness of the conduit is improved while limb
flexibility is not significantly impaired. For this condition, the spine
is preferably between 100.5% and 105% of the length of the conduit.

[0080]A second preferred embodiment of the present invention will now be
described in detail with reference to FIGS. 11 and 12. FIG. 11 discloses
a breathing circuit limb including an outer reinforcing sheath 27
covering the entire length of the breathing conduit.

[0081]The reinforcing sheath 27 is preferably a braided mesh surrounding
the breathing circuit limb and is bonded to the limb only at the ends
where the breathing conduit is inserted into the end connectors. All
styles of breathing circuit limb end connector described above are
suitable for receiving and securing a reinforcing mesh according to the
second embodiment of the present invention. In each case the reinforcing
sheath is located outside the breathing conduit wall and is secured at
and around the end connector at the same time as the conduit wall is
secured. FIG. 11 shows an end connector having a breathing conduit
receiving portion which includes a raised external thread for cooperation
with the helical reinforcing bead of the conduit. The end connector may
also include a recess or groove for receiving a reinforcing spine as
described in the first preferred embodiment of the present invention.
During assembly the thin walled breathing conduit is threaded over the
end connector conduit receiving portion via the interaction between the
breathing conduits helical reinforcing bead and the end connectors raised
external thread. A tubular braided reinforcing mesh 27 is then installed
over top of the breathing conduit. FIG. 11 shows a reinforcing mesh 27
over a portion of breathing conduit. In FIG. 11, the end portion of the
mesh is not yet pulled all the way over the conduit ready for securing
via retaining collar 29.

[0082]As previously described in the first preferred embodiment of the
present invention two preferred methods of securing the breathing circuit
limb components are disclosed. The first method employs a securing collar
positioned over the breathing conduit and the conduit receiving portion
of the end connector, forming an annular space which is then filled with
a suitable adhesive such as EVA glue. The alternative securing method
described in the first preferred embodiment of the present invention may
be adapted to secure the braided reinforcing sheath into the end
connector. In this overmoulded alternative the assembled components are
inserted into an injection mould cavity so that a collar may be
overmoulded to perform the functions of securing and sealing the
components of the breathing circuit limb. In this method the retaining
sleeve is substituted for the overmoulded resin.

[0083]The braided reinforcing mesh may be applied to a breathing conduit
as an online process where the braid is formed at the same time as the
conduit is formed, or alternatively a prebraided tube may be applied to a
breathing conduit in a separate process. The braided mesh may be
fabricated from a variety of materials but is preferably polyethylene
terephthalate monofilaments.

[0084]In use the braided sheath contributes significantly to the tensile
and torsional stiffness of the breathing circuit limb. While there is no
bonding between the reinforcing mesh and the breathing circuit limb along
the length of the conduit, it has been found that the braided reinforcing
mesh significantly improves torsional rigidity of the breathing circuit
limb. In this embodiment it is preferable to choose the material, number,
weave pitch and gauge of the braided filaments to improve the conduits
stiffness. When the limb is loaded in tension, the stretching of the
reinforcing mesh causes the mesh tube to constrict radially. This radial
constriction is resisted by the helical reinforcing bead of the breathing
conduit resulting in a strain limiting effect for the breathing circuit
limb. This effect significantly improves the breathing circuit limb
strength and stiffness against axial tensile forces. The outer mesh
sheath also provides an additional advantage by reducing direct contact
between the user/environment and the outer surface of the breathing
conduit tube, therefore reducing the risk of puncture and damage. This
feature significantly improves the durability of the breathing circuit
limb, and is especially suitable for conduits with very thin walls, such
as those which may be found in breathable walled limbs.